1. Field of the Invention
The present invention relates to an elastically coupled joint capable of absorbing vibration, and in particular to an improvement on an elastically coupled joint employed in a steering mechanism of a vehicle.
2. Related Background Art
FIGS. 6 and 7 show an example of an elastically coupled joint provided in a steering shaft for absorbing the vibration of wheels resulting from the movement of a vehicle or the vibration of engine, thereby isolating the steering wheel from such uncomfortable vibration. In particular, FIGS. 6 and 7 show a torque transmitting assembly, as disclosed in the U.S. Pat. No. 3,878,695, composed of a sleeve 15 of an elastomer fitted in a radially compressed state between a shaft 13 and a concentric tubular member 14, and a washer 17 fixed on said shaft and having a projection 16 loosely engaging with a notch provided at an end of said tubular member.
In another example of prior technology Japanese Laid-open Utility Model No. 57-17872 discloses a damper device for a steering shaft, which is constructed by inserting an inner tube with an oval cross section into an outer tube with a circular cross section, filling the gap therebetween with a vibration-absorbing member such as rubber, press-fitting a shaft with an oval cross-section into said inner tube with an elastic member, forming a penetrating hole in said, tube, and inserting a stopper pin in said penetrating hole and through said inner tube and said shaft in such a manner as to allow a relative movement between said inner tube and said outer tube.
In the torque transmitting assembly disclosed in the above-mentioned U.S. Pat. No. 3,878,695, the notch of the tubular member engaging with the projection of the washer is provided at an end of the tubular member opposite to the end thereof constituting the yoke of a universal joint, and the sleeve consisting of elastomer material is directly fixed to the tubular member, so that the engaging part of the washer has to be formed outside of the sleeve, namely at the far side of the shaft. For this reason the assembly inevitably becomes long and heavy. The assembly is therefore not desirable for being incorporated in a limited space of the vehicle, and does not contribute to the weight reduction thereof. Also, in order to prevent slippage between the sleeve consisting of elastomer material and the tubular member, said sleeve has to be directly adhered to the inner face of the tubular member. However, the adhering step is difficult to automate if the shaft is relatively long, thus leading to a manufacturing increase. Also, the washer cannot be assembled with the tubular member after being fixed to the shaft in advance, but requires complicated assembling steps, with an increased cost. In addition, the circumferential gap between the projection of the washer and the notch of the tubular member is determined by the positional accuracy during assembling, so that the gaps at right and at left may become unbalanced. Consequently, the projecting portion of the washer and the notch of the tubular member are mutually engaged with a smaller torque in one rotating direction than in the other rotating direction. Thus, when a large torque is involved, for example, rotating the steering wheel while the vehicle is stopped, the rotating angle of the steering wheel until the tubular member comes into contact with the washer becomes different in both rotating directions, thereby undesirably affecting the feeling of driving. At the side with the smaller gap, the contact between metals takes place even under a small torque, thus transmitting the vibration to the steering wheel, and a vibration absorbing effect balanced in both directions cannot be achieved.
Also, in the damper device for the steering shaft disclosed in the Japanese Laid-open Utility Model No. 57-17872, a vibration absorbing material such as rubber is fixed between an inner tube and an outer tube, said outer tube is welded to the yoke, and a stopper pin pressed into the shaft is loosely fitted in an axially elongated penetrating hole provided in said outer tube. In such case, the outer tube is axially long and is not made light in weight. Also, the axially elongated penetrating hole in the outer tube and the hole provided in the shaft for pressing in the stopper pin cannot be simultaneously prepared in other, the components have to be separately manufactured and then assembled. Thus, due to manufacturing error or assembling error, the circumferential gap at either side of the stopper pin cannot be made equal, so that the above-mentioned drawbacks are unavoidable.